The present invention relates to the distribution of natural gas or the like and, in particular, to the regulation of the pressure at low pressure regulator stations located at selected points in the distribution network of a gas supply utility.
In a typical gas distribution system the gas is fed into a network of pipe lines fanning out from a central supply area and its pressure is regulated at various points along the network. To ensure against extinguishment of flames throughout the system with the attendant dangers of explosion and asphyxiation, pressures have to be maintained such that at least a predetermined minimum pressure exists at the extremities of the network for all pressure drops encountered over the range of demand. Since the demand changes with time of day, day of the week and ambient temperature, it has heretofore been the practice to maintain pressures at supply points at a sufficiently high level that the minimum pressure at the system low points would never fall below the pressure established as a safe minimum. A typical standard requires a minimum pressure of 4.5 inches water column (w.c.), which, based upon experience, has necessitated that the supply point pressure be maintained at least at about 9 or 10 inches w.c.
The pressure required at a regulator station varies from hour to hour depending on the changing load. The regulator outlet pressure required at the peak hours and the off-peak hours can differ by up to 3 inches w.c. Thus, during most of the day, a higher pressure than that required to satisfy the off peak demand must be maintained to handle the demand during the peak hours.
Unfortunately, the higher pressures contribute to increased loss to the public utility. Since the gas meters used at customer sites are not pressure compensated, gas delivered at say 8 inches w.c. as compared to that at 6 inches w.c. is under-registered by about 0.5%. In addition, the network piping is not entirely leak proof and leakage increases in direct proportion to increasing pressure. This adds to lost and unaccounted for gas. Leakage represents real cost, both in terms of the value of gas lost from the system and the cost to repair those leaks considered hazardous.